1. Field of the Invention
This invention relates generally to the field of measurement circuit design, and more particularly, to an improved system and method for measuring the charging and discharging current in a battery-containing electrical system.
2. Description of the Related Art
Measurements are often performed to determine the total power being delivered by a battery to a load, or to determine the charging and discharging current of a battery system. In performing such measurements, it is desirable to accurately measure very small drops across a sense resistor that is carrying current from the battery to the load or from a charger to the battery. Both sides of the resistor may be at very high voltages depending on the battery used. Conventional Lithium ion (Li-ion) batteries in computers have DC voltages of 12V and higher. The drop across the sense resistor can be anywhere from microvolts to 100 mV.
According to the prior art, high side current measurements generally use an amplifier to amplify the voltage drop across the sense resistor and reference the amplified signal to ground, e.g., as shown in FIG. 1. (In FIG. 1, the amplifier is the device labeled “AMP”.) The amplifier is typically configured to achieve its amplifying effect based on the gain inherent in transistors, e.g., bipolar junction transistors or field effect transistors. The amplifier makes it easy to provide the amplified signal to an analog-to-digital converter (ADC). The amplifier constitutes an error source in the signal path, and hence, its presence makes the measurement less accurate.
Many other problems and disadvantages of the prior art will become apparent to one skilled in the art after comparing such prior art with the present invention as described herein.